feat(transformers): directive aliases in Dart transformers (fix #1747)

modules/angular2/src/transform/common/names.dart

@@ -6,6 +6,9 @@ const REFLECTOR_VAR_NAME = 'reflector';
 const TRANSFORM_DYNAMIC_MODE = 'transform_dynamic';
 const DEPS_EXTENSION = '.ng_deps.dart';
 const META_EXTENSION = '.ng_meta.json';
+// TODO(sigmund): consider merging into .ng_meta by generating local metadata
+// upfront (rather than extracting it from ng_deps).
+const ALIAS_EXTENSION = '.aliases.json';
 const REFLECTION_CAPABILITIES_NAME = 'ReflectionCapabilities';
 const REGISTER_TYPE_METHOD_NAME = 'registerType';
 const REGISTER_GETTERS_METHOD_NAME = 'registerGetters';
@@ -20,6 +23,10 @@ String toMetaExtension(String uri) =>
 String toDepsExtension(String uri) =>
     _toExtension(uri, const [META_EXTENSION, '.dart'], DEPS_EXTENSION);
 
+/// Returns `uri` with its extension updated to [ALIAS_EXTENSION].
+String toAliasExtension(String uri) =>
+    _toExtension(uri, const [DEPS_EXTENSION, '.dart'], ALIAS_EXTENSION);
+
 /// Returns `uri` with its extension updated to `toExtension` if its
 /// extension is currently in `fromExtension`.
 String _toExtension(

modules/angular2/src/transform/common/ng_meta.dart

@@ -0,0 +1,88 @@
+library angular2.transform.common.ng_meta;
+
+import 'package:angular2/src/render/api.dart';
+import 'package:angular2/src/render/dom/convert.dart';
+import 'logging.dart';
+
+/// Metadata about directives and directive aliases.
+///
+/// [NgMeta] is used in three stages of the transformation process. First we
+/// store directive aliases exported from a single file in an [NgMeta] instance.
+/// Later we use another [NgMeta] instance to store more information about a
+/// single file, including both directive aliases and directives extracted from
+/// the corresponding `.ng_deps.dart` file.  Further down the compilation
+/// process, the template compiler needs to reason about the namespace of import
+/// prefixes, so it will combine multple [NgMeta] instances together if they
+/// were imported into a file with the same prefix.
+///
+/// Instances of this class are serialized into `.aliases.json` and
+/// `.ng_meta.json` files as intermediate assets to make the compilation process
+/// easier.
+class NgMeta {
+  /// Directive metadata for each type annotated as a directive.
+  final Map<String, DirectiveMetadata> types;
+
+  /// List of other types and names associated with a given name.
+  final Map<String, List<String>> aliases;
+
+  NgMeta(this.types, this.aliases);
+
+  NgMeta.empty() : this({}, {});
+
+  bool get isEmpty => types.isEmpty && aliases.isEmpty;
+
+  /// Parse from the serialized form produced by [toJson].
+  factory NgMeta.fromJson(Map json) {
+    var types = {};
+    var aliases = {};
+    for (var key in json.keys) {
+      var entry = json[key];
+      if (entry['kind'] == 'type') {
+        types[key] = directiveMetadataFromMap(entry['value']);
+      } else if (entry['kind'] == 'alias') {
+        aliases[key] = entry['value'];
+      }
+    }
+    return new NgMeta(types, aliases);
+  }
+
+  /// Serialized representation of this instance.
+  Map toJson() {
+    var result = {};
+    types.forEach((k, v) {
+      result[k] = {'kind': 'type', 'value': directiveMetadataToMap(v)};
+    });
+
+    aliases.forEach((k, v) {
+      result[k] = {'kind': 'alias', 'value': v};
+    });
+    return result;
+  }
+
+  /// Merge into this instance all information from [other].
+  void addAll(NgMeta other) {
+    types.addAll(other.types);
+    aliases.addAll(other.aliases);
+  }
+
+  /// Returns the metadata for every type associated with the given [alias].
+  List<DirectiveMetadata> flatten(String alias) {
+    var result = [];
+    var seen = new Set();
+    helper(name) {
+      if (!seen.add(name)) {
+        logger.warning('Circular alias dependency for "$name".');
+        return;
+      }
+      if (types.containsKey(name)) {
+        result.add(types[name]);
+      } else if (aliases.containsKey(name)) {
+        aliases[name].forEach(helper);
+      } else {
+        logger.warning('Unknown alias: "$name".');
+      }
+    }
+    helper(alias);
+    return result;
+  }
+}